When it comes to considering the burden that transport imposes on the environment, it pays to look at the full impact of the associated infrastructure and supply chains. Or so say Mikhail Chester and Arpad Horvath from the Department of Civil and Environmental Engineering at the University of California, Berkeley.
In a recent paper in the journal Environmental Research Letters the researchers complain that "Most current decision-making relies on analysis at the tailpipe, ignoring vehicle production, infrastructure provision, and fuel production required for support."
http://stacks.iop.org/ERL/4/024008
The researchers try to cut their way through this ignorance with a "comprehensive life-cycle energy, greenhouse gas emissions, and selected criteria air pollutant emissions inventory for automobiles, buses, trains, and airplanes in the US, including vehicles, infrastructure, fuel production, and supply chains".
Unravelling this grammatically tortured pile suggests that they have counted the emissions of greenhouse gases and other air pollutants for every bit of the chain for different modes of transport, taking in what they call "non-operational components," such as the emissions generated when building all those roads and railway lines.
After they have done their number crunching – the paper has the equations – the researchers conclude that "total life-cycle energy inputs and greenhouse gas emissions contribute an additional 63 per cent for onroad, 155 per cent for rail, and 31 per cent for air systems over vehicle tailpipe operation".
As you would expect, the media, when fed a press release on the paper, pick on the juicy bits. One report, for example, reads the paper as telling us that public transport is not as green as we'd like to think. Another decided that flying is not quite so severe a crime against the planet as some people suggest.
It is, though, stretching it to use this research to choose between transport modes. The paper is really about the importance of looking beyond the tailpipe and how to go about it. The researchers focus on a few examples and these tells us very little about the picture in, say, a European country.
For example, the researchers studied three cars that are typical of those seen on roads in the USA. Given that the vehicle preferences of Americans and the nature of the US road network are very different from what is found in Europe, for example, it would be unwise to read too many lessons into this analysis for the rest of the world.
In reality, counting life-cycle emissions is not a new idea. In part two of The King Review of low-carbon cars, Professor Julia King wrote: "Policy must target overall CO2 emissions to ensure that tailpipe emissions are not reduced at the expense of emissions elsewhere."
http://www.hm-treasury.gov.uk/bud_bud08_king_review.htm
A thorough study of transport and climate change has to include plenty of other factors. Rail travel certainly looks bad with its massive overhead. (Concrete carries a lot of the blame on this front.) But how far do people drive to get to the airport or station to take that plane or train? Does life-cycle assessment include this and the many other factors involved in transport?
The researchers are right to point out that "reduction goals should consider non-operational processes". But that is just the beginning. Unfortunately, looking beyond the tailpipe needs a very large microscope.
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